This application claims the priority benefit of Taiwan application serial no. 89105442, filed Mar. 24, 2000.
1. Field of Invention
The present invention relates to an objective lens actuator structure. More particularly, the present invention relates to a wire-suspended objective lens actuator structure and a method of assigning current pathways.
2. Description of Related Art
Most photosensitive recording/regenerating devices contain an optical pickup head. To operate a recording/regenerating device, a beam of laser from a light source is passed into the object lens of an optical pickup head. The light beam forms a focus point at the data layer inside an optical disk. On reflecting from the data layer, the laser beam is intercepted by the optical pickup head again so that embedded data on the optical disk is retrieved.
The actuator device that drives the optical pickup head has a lens holder. In order for the optical pickup head to access data on an optical disk, a focusing coil for controlling the focus and a tracking coil for controlling the tracking must be installed on the lens holder. Currents are passed into these two coils to produce driving power in the magnetic field so that focusing and tracking are in control. Since the lens holder is the target of control for the focusing and the tracking system, inappropriate suspension renders control of the lens holder very difficult. Hence, it is important to take note of the method of channeling current into the lens holder because the current-position transfer function is likely to be affected. Most wire-suspended actuator device utilizes the conductive wires to suspend the lens holder and to input currents.
FIG. 1 is a perspective view of a conventional wire-suspended objective lens actuator structure. FIG. 2 is a side view of the conventional wire-suspended objective lens actuator structure in FIG. 1. As shown in FIGS. 1 and 2, two U-shaped irons 101 are vertically erected on each side of a base plate 100. The vertical branch of the U-shaped irons 101 closer to the edges of the base plate 100 is referred to as the outer branch. Similarly, the vertical branch of the U-shaped magnetic irons 101 closer to the middle of the base plate 100 is referred to as the inner branch. Two magnetic blocks 102 are attached to the respective inner sides of the outer branches of the U-shaped irons 101 for generating magnetic fields that cause the lens holder 104 to float on the base plate 100. A focusing coil 106 and a tracking coil are attached to each side of the lens holder facing the U-shaped irons 101. The wires inside the focusing coil 106 runs around in a plane that are parallel to the base plate 100. The inner branch of the U-shaped irons 101 passes through the center of the respective focusing coil 106 assembly. On the other hand, the wires inside the tracking coil 108 runs around in a plane that are perpendicular to the base plate 100. The tracking coils 108 are positioned between the magnetic block 102 and the inner branch of the U-shaped irons 101. The lens holder 104 is suspended over the base plate 100 through the control wire 110 of the focusing coil 106, the control wire 112 of the tracking coil 108, the ground wire 114 of the focusing coil 106 and the ground wire 116 of the tracking coil 108.
FIG. 3 is a sketch of the assigned current pathways in a conventional wire-suspended objective lens actuator structure. Amongst the four conductive wires shown in FIG. 3, two conductive wires are used for controlling the focusing coil 106 and the other two conductive wires are used for controlling the tracking coil 108. Current flows into the focusing coil 106 via the control terminal 110 and emerges from the focusing coil 106 via the ground terminal 116. Similarly, current flows into the tracking coil 108 via the control terminal 112 and emerges from the tracking coil 108 via the ground terminal 116.
As data packing density inside an optical disk continues to rise, resolution of the optical reading system must also increase. Hence, desired perpendicularity between the light axis and the disk surface is correspondingly higher. To control the slant angle of the laser beam, an electrical servo system must be used. Otherwise, precision demanded by the optical system is so high that it is almost impossible to manufacture. In a conventional wire-suspended optical pickup head actuator structure, all four conductive wires are used up by the focusing coil and the tracking coil. Therefore, there is no wires left for installing slant adjustment coils.
Accordingly, one object of the present invention is to provide a wire-suspended objective lens actuator structure whose lens holder is able to bear not only a focusing coil for focusing and a tracking coil for tracking, but also a slant adjustment coil for adjusting the slant angle. The wire-suspended actuator structure can be applied to a high-density optical disk and a high-precision optical system. When the optical disk somehow moves away from the optical axis during spinning, the slant adjustment coil is able to adjust the lens holder so that the lens holder remains parallel to the optical disk. Hence, correct data can be read from the optical disk as usual.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method for assigning current pathways to the wire-suspended actuator structure. Four conductive wires are used to control three sets of coils. Each of the three conductive lines is used for controlling the focusing coil, the tracking coil and the slant adjustment coil respectively. The fourth conductive wire is a common ground terminal for three sets of coils.
This invention also provides a wire-suspended objective lens actuator structure and a method of assigning current pathways such that the ground terminal of the original independent focusing coil and tracking coil are combined. The freed-up ground wire is used as a conductive wire that leads to one of the terminals of a slant adjustment coil. The other terminal of the slant adjustment coil is connected to the common ground terminal of the focusing and tracking coil. The control terminal of the focusing coil, the tracking coil and the slant adjustment coil are each connected to a differential voltage-output current amplifier circuit or to a differential voltage-output voltage amplifier circuit respectively. Using a small differential voltage, focusing, tracking and slant adjustment of the lens holder are possible.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.